[fix] validate advance only if invoice total is positive
[fix] validate advance only if invoice total is positive

indictranstech/erpnext,indictranstech/osmosis-erpnext,indictranstech/erpnext,Aptitudetech/ERPNext,anandpdoshi/erpnext,ShashaQin/erpnext,anandpdoshi/erpnext,gangadharkadam/v6_erp,gangadharkadam/v6_erp,aruizramon/alec_erpnext,indictranstech/osmosis-erpnext,indictranstech/erpnext,ShashaQin/erpnext,sagar30051991/ozsmart-erp,mahabuber/erpnext,njmube/erpnext,gsnbng/erpnext,sagar30051991/ozsmart-erp,njmube/erpnext,njmube/erpnext,gsnbng/erpnext,indictranstech/osmosis-erpnext,indictranstech/osmosis-erpnext,sagar30051991/ozsmart-erp,mahabuber/erpnext,anandpdoshi/erpnext,aruizramon/alec_erpnext,gsnbng/erpnext,geekroot/erpnext,geekroot/erpnext,gsnbng/erpnext,mahabuber/erpnext,aruizramon/alec_erpnext,aruizramon/alec_erpnext,indictranstech/erpnext,ShashaQin/erpnext,geekroot/erpnext,ShashaQin/erpnext,njmube/erpnext,gangadharkadam/v6_erp,anandpdoshi/erpnext,sagar30051991/ozsmart-erp,geekroot/erpnext,mahabuber/erpnext,gangadharkadam/v6_erp